The invention relates to electrical connections, to the monitoring of electrical connections using the presence of heat as an indication of the performance or integrity of the connections, and to the use of thermochromic materials to visually monitor local changes in temperature, particularly within the electrical connections.
Thermochromic materials, including liquid crystals and leuco dyes in the form of paints or inks, respond to temperature changes by changing color. The materials change color as a function of temperature, typically by reflecting different portions of the white light spectrum. The color changes of some such materials are reversible and others permanent. Some such materials vary through a range of colors and others toggle between just two colors. The color changes can occur throughout the visible spectrum and can alter between opaque or clear. The activation temperatures at which the color changes occur also vary among the thermochromic materials.
These thermochromic materials have been used in a variety of thermochromic applications for monitoring temperature or temperature related events. Liquid crystal thermometers have been used for measuring body temperature and room temperature, as well as the temperatures of refrigerators, aquariums, and propane tanks. Leuco dyes, which usually vary between opaque and clear, are more often used as more general indications of temperature change. For example, leuco dyes have been used for such purposes as mood rings, battery testers, and temperature threshold indicators on microwavable foods or coffee cups.
Liquid crystal materials have also been used in more advanced thermochromic systems involving image acquisition and calibrated analysis of thermochromic color changes. For example, thermochromic liquid crystal based thermography systems have been used for monitoring local temperatures and temperature gradients of electronic devices. Thermochromic temperature maps can be used to identify the hottest areas or parts of electronic devices, referred to as “junction temperature”, for evaluating such issues as reliability, operational integrity, and thermal resistance.